Some Massachusetts voters see Sen. Edward Markey as potentially vulnerable to a primary challenge, and one group is even trying to persuade U.S. Rep. Joe Kennedy to run for his seat.Markey, a Democrat, has represented Massachusetts in Congress for decades — first in the House before winning John Kerry's former Senate seat in 2013 — but the state saw an incumbent lose just last year as Democrats elected more women and minorities.

Ayanna Pressley defeated longtime incumbent U.S. Rep. Michael Capuano in the Democratic primary and went on to become Massachusetts' first black woman elected to the U.S. House.